Automobile diagnostic data, such as Diagnostic Trouble Codes (DTCs), form compact, informative messages. Diagnostic data was designed to allow vehicle controllers to indicate a system fault and/or a need for repair. Although the DTC is in ‘Active’ or ‘Confirmed’ status for the key cycle in which the fault occurred, most DTCs then revert to a ‘History’ or ‘Aging’ status for a number of key cycles so that evidence of the fault will still be available, even if the vehicle is inspected by a technician weeks after the fault.